1. Field of the Invention
This invention relates to a novel crosslinkable, wear resistant binder for a charge transport layer of a photoconductor used in electrophotography. More in particular, the invention relates to a binder for a charge transport layer comprised of one or more poly(arylene ether alcohols) crosslinked with one or more polyisocyanates.
2. Description of Related Art
In the art of electrophotography, an electrophotographic plate comprising a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the surface of the photoconductive insulating layer. The plate is then exposed to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic toner particles on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving member such as paper.
Electrophotographic imaging members are usually multilayered photoconductors that comprise a substrate support, an electrically conductive layer, an optional hole blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer in either a flexible belt form or a rigid drum configuration. For most multilayered flexible photoconductor belts, an anti-curl layer is usually employed on the back side of the substrate support, opposite to the side carrying the electrically active layers, to achieve the desired photoconductor flatness. One type of multilayered photoconductor comprises a layer of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder.
U.S. Pat. No. 4,265,990 discloses a layered photoconductor having separate charge generating (photogenerating) and charge transport layers. A charge generating layer (CGL) is capable of photogenerating holes and injecting the photogenerated holes into a charge transport layer (CTL). The photogenerating layer utilized in multilayered photoconductors include, for example, inorganic photoconductive particles or organic photoconductive particles dispersed in a film forming polymeric binder. Inorganic or organic photoconductive material may be formed as a continuous, homogeneous photogenerating layer.
Examples of photosensitive members having at least two electrically operative layers including a charge generating layer and diamine containing transport layer are disclosed in U.S. Pat. Nos. 4,265,990, 4,233,384, 4,306,008, 4,299,897 and 4,439,507. The disclosures of these patents are incorporated herein in their entirety.
Charge transport layers typically comprise a charge transport material dispersed in a polycarbonate binder such as PCZ 400 manufactured by Mitsubishi Gas Chemical Company, Inc. However, such polycarbonate binders suffer from a fast, nearly catastrophic wear rate of 8 to 9 microns per 100 kilocycles when the photoconductor is charged using a bias charging roll (BCR) to charge the photoconductor and a considerable corotron CTL wear rate of .about.2.7 microns per 100 kilocycles when using a corotron to charge the photoconductor.
Wear rate is a significant property in that it limits the life of the photoconductor, and photoconductor replacement in electrostatographic devices such as copiers and printers is very expensive. It is thus very significant to limit wear of the photoconductor so as to achieve a long life photoconductor, particularly with respect to small diameter organic photoconductor drums typically used in copiers and printers. In such small diameter drums, 100 kilocycles translates into as few as 10,000 prints. CTL wear results in a considerable reduction in device sensitivity, which is a major problem in office copiers and printers that typically do not employ exposure control.
There remains a serious need for a photoconductor, particularly an organic photoconductor drum, with a long life of at least 100,000 prints, which translates into approximately a minimum of 1 million photoconductor spin cycles.